1. Field of the Invention
The present invention relates to a shielding box provided for an electronic control apparatus such as an image-forming machine which is a composite machine as represented by an electrostatic copier, a laser printer or a facsimile.
2. Description of the Related Art
A wiring board on which there is arranged a digital circuitry of an image-forming machine which is a composite machine such as an electrostatic copier, a laser printer or a facsimile, is, generally, contained in a shielding box to satisfy the Standards for Radiant Electromagnetic Waves. A CPU is mounted on the wiring board. Accompanying the advancement in the high-speed processing of modern electronic equipment, the clock frequency of the CPU is ever increasing, too, accompanied, however, by an increase in the amount of heat generated by the CPU and an increase in the surface temperature. If this state is left to stand, the CPU undergoes the thermal runaway and the electronic equipment malfunctions. Therefore, cooling becomes necessary.
JP-A-2002-23597 discloses an image-forming machine having a constitution in which a cooling fan is mounted on a shielding box, the external air is taken into the machine body by the cooling fan, and the external air is partly fed into the shielding box to cool the wiring board. In this shielding box, the external air taken in by the cooling fan is partly fed into the shielding box without, however, primarily cooling the surface of the CPU. In particular, when a plurality of, e.g., two pieces of wiring boards are mounted maintaining a distance and facing each other on the machine body being contained in the shielding box and when the CPU is arranged on the wiring board positioned on the side of the machine body, it becomes necessary to take a countermeasure such as providing a dedicated duct for cooling the CPU or increasing the blowing rate of the cooling fan to primarily cool the surface of the CPU. As a result, the constitution becomes complex and bulky boosting up the cost. The above technical problem similarly exists even when the member that must be primarily cooled is a particular member that needs cooling other than the CPU.